The California earthquake of April 18, 1906 is one of the most significant earthquakes of all time. The earthquake ruptured approximately 296 miles of the San Andreas earthquake fault from Northwest of San Juan Bautista to the triple junction at Cape Mendocino. At 5:12 AM local time, a shock brand throughout the San Francisco Bay area. Approximately 20 to 25 seconds later, violent shocks shook the city. The epicenter of the earthquake was right near San Francisco. The earthquake was recorded in Gottingen, Germany, 91 km away!

The casualty accounts vary widely, but it is generally accepted that more than 3000 people died in the event. A 1906 U.S. Army report recorded 498 deaths in San Francisco, 64 in Santa Rosa, and 102 deaths near San Jose. The population of San Francisco in 1906 was approximately 400,000. 225,000 people were left homeless, over one half of the population. 28,000 buildings were destroyed, and tent cities became the abode for many.

Fires ravaged the city of San Francisco for more than three days causing more damage then realized by the earthquake. The burned area covered approximately 4.7 square miles. Based on a NOAA report,

Broken and leaking gas lines were the predominant cause of fires in the city. The fire department was at a disadvantage in fighting the fire. Fire Chief Dennis T. Sullivan died in the earthquake, leaving the city’s firefighters without effective leadership. It is reported that the firefighters used dynamite to destroy selected houses in an effort to stop the spread of the conflagration. Unfortunately, the explosions created more damage. Water mains below the city streets were rendered useless because the earthquake ruptured the pipes, causing the water pressure to drop to unusable levels.

It is also believed that some people set their own houses on fire in hopes of insurance compensation for fire. Insurance companies at the time did not indemnify policyholders in the event of an earthquake, but did for fire.

Many experts claimed that 90% of the damage in San Francisco was as a result of the ensuing fires. Approximately 490 city blocks were destroyed! The city was in a state of disarray with thousands homeless, tent cities springing up, and lawlessness running rampant. Eventually, the U.S. Army was activated to assist with the cleanup and control of the city.

San Francisco began rebuilding immediately. Reconstruction was mostly completed by 1915, nine years later.

The next article in a series discussing fire sprinkler system inspection testing and maintenance is published in ASSE Fireline.

Inspection, testing and maintenance of dry pipe valves and dry pipe systems are critical to maintaining effective fire protection. Dry pipe valves are used in areas subject to freezing temperatures.

This article focuses on Chapter 13, Valves, Valve Components and Trim, and assumes that all items discussed in previous articles regarding valve inspection and testing, records plans and calculations and impairments to the fire system have been completed. This article discusses items that apply specifically to dry pipe valves.

A dry pipe sprinkler valve is a special valve that prevents the pressurized water in the fire mains from entering the sprinkler system piping. Normally, this is accomplished by filling the system with air. Most valves use a differential method of keeping the valve shut, and generally, the differential is 5:1 or 6:1. This means that 5 or 6 psi of water pressure is held back by 1 psi of air pressure. In the event of a fire in which a sprinkler head actuates, the air pressure in the system decreases until the valve trips. The trip pressure in a 5:1 dry pipe valve at 60 psi of water pressure is 12 psi. As the air pressure dips below 12 psi, the valve will trip, allowing water to enter the sprinkler piping and eventually exit through the open sprinkler head. A safety factor, usually about 20 to 25 psi, is maintained above the trip pressure to help prevent false trips. An air compressor, or other means of maintaining pressure in the system, is arranged to automatically maintain adequate air pressure.

Components of dry pipe valves are discussed, described, and explained. Testing procedures for properly tripping a dry valve is outlined, as well as an explanation of how to reset typical differential dry valves.